Cancer is a condition that has afflicted humanity for thousands of years. Cancer was first described by ancient Egyptians, and evidence of cancer has been discovered in bone fossils. It is still a major public health problem and one of the leading causes of death worldwide. Traditional cancer treatments, including surgery, chemotherapy, and radiotherapy, are usually non-specific and have some limitations. Thus, these problems urged scientists to develop newer treatment modalities. In recent decades, our discoveries about the relationship between the immune system and cancer have led to the development of a novel treatment strategy called cancer immunotherapy. Cancer immunotherapy is a type of treatment that uses the components of the patient’s own immune system to target tumor cells. Currently, there are several types of cancer immunotherapy approaches, such as cytokine therapy, monoclonal antibodies (mAbs), adoptive cellular immunotherapy (ACI), cancer vaccines, and immune checkpoint inhibitors, which all have revolutionized cancer treatment. This chapter will provide an overview of the history of cancer immunotherapy and outline the role of the immune system in cancer. Also, different cancer immunotherapy approaches will be briefly discussed.